Starting control for electric discharge devices



Oct. .1, 1946. TOWNSEND I 2,408,493

STARTING CONTROL FOR ELECTRIC DISCHARGE DEVICES Filed Dec. 6, 1941 Fig.1. P

ML I L ooo o i lnvenfor: Mark A. Townsend by .Wm His A't't'orneg'.

Patented Oct. 1, 1946 STARTING CONTROL FOR ELECTRIC DISCHARGE DEVICES Mark A. Townsend, Cleveland Heights, Ohio, assignor to General Electric Company, a corporation of New York Application December 6, 1941, Serial No. 421,941

11 Claims. 1

This invention relates to the control of electric discharge devices, and is especially concerned with the starting of such devices. The invention is very useful in connection with fluorescent tubes or lamps of the positive column discharge type, and is hereinafter explained with particular reference to lamps of this character and their usual starting arrangements, as exemplified in U. S. Patent 1,951,112, March 13, 1934, to Wels, or Patent 2,212,427, August 20,1940, to Peters, for instance.

Ordinary tubular fluorescent lamps have electrical starting circuits which are energized and broken to start the discharge. Sometimes this has to be done several times before the discharge actually starts. For this purpose, automatic means are commonly provided which will mak and break the starting circuit indefinitely until starting is accomplished.

Through deterioration in service or as the result of accident, fluorescent lamps and other discharge devices often or eventually become incapable of starting and normal running, so that the only effect of the automatic efiorts to start such a lamp is a continual flashing in it that is veryannoying to those in the area that receives the light of the flashing lamp, besides uselessly wearing out the starter device. Usually such incapacity for starting is dueto loss of electron emission from one or both electrodes of the lamp,

which may result from dissipation or other loss of activating material on which the emission depends. The objectionable flashing of such a lamp goes on indefinitely, until the power supply is shut off, or the lamp is removed from the circuit.

The purpose of my invention is to obviate the undesirable flashing of defective lamps without interfering with repetition of the attempts to start as long as there is any reasonable promise of success. This I accomplish by rendering the starter ineffective to open the starting circuit. I have shownand explained the invention as applied to a closed glow-switch type of starter. The glowswitch illustrated is of double bimet'al type; but

the invention is equally applicable to a single and Fig. 3 is a plan or end view of the more important parts shown in Fig. 2.

Fig. 4 is a view similar to Fig. 2 illustrating an additional shunting modification.

I will first describe the portion of the circuits and apparatus shown which have heretofore been in use, and which permit the objectionable flashing of a defective lamp as described above.

Fig. 1 shows an ordinary fluorescent tube lamp L of the positive column electric discharge type with a tubular envelope Ill having spaced-apart activated thermionic cathodes H, H in its ends, which may be specially heated cathodes of usual coiledfilament type, and are shown connected across a power-supply circuit P including the usual ballast M, which also serves as a starting inductance, and the manual make-and-break switch I5. The envelope I0 may contain a lowpressure atmosphere of starting gas, such as argon at a pressure of 2 to 5 mm. of mercury, and also a vaporizable and ionizable working substance such as mercury. A supply of mercury, which may exceed the amount that will vaporize during operation of the lamp L, is indicated by a drop I! inside the envelope Ill, and an internal coating of fluorescent material or phosphor l8 on the envelope walls is also indicated. A starting and electrodeheating circuit H is shown connected across the circuit P through the filamentary cathodes I I, I I, with a starting switch S included therein, which may be of thermal type.

The general mode of operation in starting the lamp L with this circuit arrangement is that when the switch I5 is closed to turn on the lamp L, the switch device S permits flow of current through the circuit H and the cathode filaments H, II in series therein for a sufiicient length of time to preheat the cathodes to an adequate emissive temperature, and then suddenly opens the circuit H; and the resulting voltage kick across the cathodes H, II suifices to initiate discharge between them, or, in other words, starts the lamp.

As shown in Figs. 1 and 2, the thermal switch S is of glow-switch type, comprising a glass envelope 20 containing a low-pressure atmosphere of rare gas, such as neon at an absolute pressure of 50 mm. of mercury. The envelope 20 may include a stem 2| through which are sealed current leads 22, 23 that are connected to opposite sides of the circuit H, and are provided with terminals or electrodes inside the envelope between which a glow discharge takes place when the switch I5 is first closed. In the switch S here illustrated, both these terminals or electrodes consist of slender, straight approximately upright thermostatic bi-' metal strip members 25, 26 attached to the leads 22, 23, as by welding, and coacting as both temperature-responsive elements and contacts for the switch S, Accordingly, contact pieces 21, 2'! (as of molybdenum) are shown welded to the free ends of these members 25, 26. These members 25, 25 should be identical in order that they may heat and flex alike, and must be slender enough to keep the glow discharge current between them so low as to assure starting of the main discharge between the electrodes ll, ll when the contacts 27, 27 separate and break the circuit H, as explained hereinafter.

The general operation of such a switch S is that when the circuit H is energized as a result of closing the hand switch IS, a glow discharge takes place across the gap between the parts 25, 26, shunting their co-operating contacts 21, 21. The conducting path for this current flow, which produces heat to heat the thermostatic bimetals 25, 26, is provided by the gaseous discharge atmosphere in the envelope 20, already mentioned. The discharge heats the members 25, 26 until they bend sufficiently to bring the contacts 21, 21 together to touch one another, thus closing the circuit H and shorting out the glow discharge. The thus augmented flow of current in the circuit H continues long enough to heat the filamentary cathodes l l, l I to an adequate electronemissive temperature; and by the time this has been accomplished, the thermostatic members 25, 26 cool sufficiently to open the circuit H and start the main discharge between the electrodes I I, l l, as already described. After the main discharge has started, the voltage on the device S is no longer high enough to maintain any discharge across the gap between the parts 25, 26

If, however, the main discharge does not start on the voltage kick due to the opening of the circuit H by the switch S as just described, a glow discharge again takes place between the parts 25, 26, and the switch S again closes and opens, just as before; and if this effort is not successful in starting the main discharge, it is repeated, and so on. In other words, the contacts 21, 2! alternately engage and disengage, over and over again, at short intervals. If the main discharge cannot be started at all, the lamp L would (with the circuit arrangement and parts so far described) go on to flash in the objectionable manner described above.

In accordance with my invention, means of control are provided for determining the condition of the circuit H as to continuity in such a way that after reasonable efforts of the starter S to start the main discharge, a closed condition of circuit H that prevent flashing of the lamp L is established and maintained, independent and regardless of any further action or operation of starter S. For this purpose, automatic control means may be employed whose period of operation (as fixed by design and adjustment) is long enough to include whatever number of attempts by starter S may be considered reasonably worth-while; e. g., a period of some seven to ten seconds under favorable voltage conditions, embracing some five to ten attempts, say. The action of this automatic control need not be an arbitrary matter of fixed adjustment, however, but can be made responsive to the actual attempts of starter S to start the main discharge. As already mentioned, the particular control here illustrated determines the continuity of the circuit H in the positive sense-by closing itin the members 25,

order to prevent continued flashing or blinking of the lamp.

A simple control for this purpose is shown in Figs. 1, 2 and 3 as comprising an additional or extraneous shunting thermostatic bimetal strip member 30 that closes the heating circuit H more or less independently of the thermostats 25, 26, and may, as here shown, suspend their further operation when it closes said circuit. In other words, the bimetal 35 when sufficiently heated shunts both the contacts 27, 21 themselves and the path of current flow provided by the con ductive supporting members 25, 2E and the gaseous atmosphere in the envelope 20. This thermost-at 33 may conveniently (though not necessarily) coact with the members 25, 26 rather than with their leads 22, 23, and may be arranged with its opposite ends in position to engage these members. A compact and convenient arrangement is for the slender strip member 30 to be bent as shown in Figs. 2 and 3 almost into an elongated loop or oval which is disposed in a horizontal plane at a level where it surround the region of the glow discharge, and approximately perpendicular to the approximately upright members 25, 2G, with its ends adjacent the latter. The member 30 may be supported about at its own midlength by an upright wire standard 3| welded to the member 36 and fused to the glass stem 2i, and its fixed mid-portion is preferably close to the zone of the gap between the members 25, 26 where the heating effect from the discharge is greatest. As shown in Figs. 2 and 3, the memher (it has contact pieces 32, 32 (as of molybdenum) welded to its ends, both of which are free to move as the member 30 flexes in response to temperature changes.

In starting a good lamp L, the starter S functions in the usual way, just as if the control thermostat 30 were absent; 1. e., this control does not enter into the action of the starter S, even though several operating cycles of the starter S should occur before the lamp L actually starts. This is because the member 30 is heated (like 25) only during the glow discharge, and is less directly exposed to the heat of the discharge than the members 25, 26 which serve as electrodes for the discharge. In the case of a defective lamp, however, the cumulation of heat in the thermostatic member 30 due to the glow discharge while the starter switch S is open (during repeated cycles or starting attempts of the starter) causes the member 39 to flex more and more, until eventually one end of it (or one i of its contacts 32, 32) engages one of the members 25, 26, thus connecting it into this side of the glow discharge circuit. Thereafter, the glow discharge takes place between the other of the members 25, 26 and the member 38, heating the latter until it flexes into engagement with the other of the members 25, 26 thus shorting out the glow discharge, and, in effect, establishing a shunt around the glow switch S. In thus shunting the contacts 21, H, the thermostatic memher 3!! responds to heat produced by current flow in the path afforded by the gaseous atmosphere in the envelope 20, and accumulated during successive intervals or periods of such current flow, though more slowly or in a lower degree than do the bimetals 25, 25. Under this condition, the member 30 (owing to its slenderness) functions as a heating resistance and is heated by the shortcircuit current through it sufficiently to keep it flexed and maintain the shunt indefinitely. Current thus flows continuously in the circuit H,

awaits without any possibility of interruption by action of starter S, and the lamp L ceases to flash. The springs", elastic members 25, 26 yield to any pressure of the member 30, and the member 30' also yields elastically under such pressure. Thus contact is maintained as long as current flows in the circuit H, even though the members 25, 25 may cool somewhat and tend to open. 1

However, if the circuit H is tie-energized (by opening the hand switch [5, or by removing the defective lamp L and replacing it with a good one), and is allowed to remain de-energized long enough for the control thermostat 30 to cool off fully, the shunt will be opened, and the starter S will again be ready tostart the lamp in the usual manner. I

Fig. 4 illustrates a glow switch device generally similar to that in Figs. 2 and 3, but different as regards the arrangement and configuration of the extraneous control thermostat 3011. Instead of being in a horizontal plane perpendicular to the thermostatic members 25, 26, the thermostatic member 3011 is arranged in a vertical plane; and in outline it is a less complete loop, of n inverted angular U-configuration. This allows the member 30a to be made longer, to surround the region of the glow discharge more completely, and to be more effectively heated by the glow discharge. As shown, the inverted u member 30a is arranged like a door frame around the members 25, 26, in a plane approximating the planes of these members, and the upper end of its supporting wire 3| is bent over across its horizontal middle segment. When this thermostat 30a closes, its free ends (or their contacts 32, 32 en-' gage against the edges of the fixed lower ends of the members 25, 26, which are Virtually mere ends of the leads 22, 23.

In Fig. 4, various parts and features are marked with the same reference numerals as in Figs. 1-3, in order to dispense with repetitive description, a distinctive letter being added where such distinction appears desirable. The operation of the device as shown in Fig. 4 is essentially the same as already described in connection with Figs. 2 and 3. I

For the convenience of those wishing to use my invention, illustrative particulars of a device S of the Fig. 4 type are here given:

The thermostatic strip members 25, 26' may be formed of the bimetal commercially known as Chace #3300 bimetal, composed of laminae of Invar, an alloy of 64'per cent iron and 36 per cent nickel, and of nickel, in equal thicknesses, welded together and coated with zinc on both sides. Each of these strips 25, 26 may be 0.015 inch thick, inch wide, and 0.43 inch long, and the normal gap between their contacts 21, 21 when they are at ordinary atmospheric temperature may be 0.022 inch. The thermostatic strip member 30a may be formed of the bimetal commercially known as Chace #2400 bimetal, composed of laminae of the Invar above mentioned and of chrome iron (which is an alloy of '75 per cent iron, 22 per cent nickel, and 3 per cent chromium) in equal thickness, welded together but uncoated. This strip 30a may be 0.004 inch thick, inch wide, and 1.18 inch long before being bent as shown in Fi 4. In its bent form, its parallel legs may be 0.44 inch long each, and spaced 0.30 inch apart, so that its horizontal top portion may be 0.30 inch long. The distance between this top portion and the upper corners of the members 25, 26 may be 0.04 inch, and the gaps between the parallel legs and the lower outer corners of the members 25, 25 may e 117 inch each at ordinary atmospheric temperature. With a filling of neon at an absolute pressure of 50 mm. of mercury, and zinc-coated members 25, 26, such a glow-switch is especially well adapted for use with a standard -watt fluorescent tube of positive column type. For lamps of other wattages, some variations of design and of the gas filling and its pressure may be found advisable. In particular, the zinc coating on the members 25, 25 and the nature and pressurepr the gas filling influence the glow voltage and the closing time of the device, and the zinc coating itself stabilizes the glow voltage and tends to reduce the time of operation of the switch. Moreover, it may be desirable to place a small amount of uranium oxide (e; g, 20 mg.) on the interior surface of the switch envelope 2i], at it's top (as indicated at 35), in order to make the operation of the switch independent of whether it is in darkness or exposed to the light, as set forth in applicationSerial No. 403,572, filed July 22, 1941, by Basil N. Clack, and assigned to the assignee of this application.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. The combination of an electric discharge device having a starting circuit comprising aura: matic switch means responsive to energization of the circuit for interrupting it to start a discharge in the device, and extraneous shunting means also responsive to energization of the circuit for closing the circuit independently of said switch means and suspending further operation of the latter after repeated operation of the switch means has failed to start the discharge.

2. The combination of an electric discharge device having spaced electrodes, a starting circuit for said device comprising automatic switch means connected across and between said electrodes and responsive to energization of the circuit for interrupting it to start a discharge between said electrodes, and extraneous shunting means also responsive to energization of the circuit for closing a shunt circuit between said electrodes around the switch means and suspending further operation of the latter after repeated operation of the switch means has failed to start the discharge. a

3. The combination of an electric discharge device having spaced electrodes, a starting circuit for said device comprising automatic switch means connected across and between said elec-' trodes and responsive to energization of the circuit for interrupting it to start a discharge between said electrodes, and automatically resettable extraneous shunting means also responsive to energization of the circuit for closing a shunt circuit between said electrodes around the switch means and suspending further operation of the latter after repeated operation of the switch means has failed to start the discharge, said shunting means being constructed and arranged to maintain its closed circuit position only so long as current continues to flow through it.

4. In combination, an electric discharge device having spaced electrodes adapted to be preheated by current flow therethrough, a ballast for said device, means including said ballast for connecting one end of each of said electrodes with a source of current supply, and thermal switch means comprising co-operating contacts connected between the other ends of said electrodes and including heat supplying means and means responsive to the heat produced by said heat supplying means for alternately causing one of said contacts to engage and disengage the other contact and thereby attempt to start the device, and thermostatic shunting means responslve to the resulting current flow for closing a shunt circuit around the switch contacts upon accumulation of heat therein during a plurality of successive attempts of the switch to start the device.

5. In combination with an electric switch comprising means for automatically and repeatedly closing and opening its contacts, extraneous shunt means operable upon energization of the switch for closing a shunt circuit around the switch contacts after a predetermined period of operation of the switch.

6. In combination with a thermal switch comprising means for supplying heat to automatically and repeatedly close and open its contacts, extraneous shunt means responsive to the heat produced by said heat supplying means for closing a shunt circuit around the switch contacts upon accumulation of heat therein during a predetermined period of operation of the switch.

'I. In combination with a thermal switch comprising means for supplying heat to automatically and repeatedly close and open its contacts, extraneous shunt means responsive to the heat produced by said heat supplying means for closing a shunt circuit around the switch contacts upon accumulation of heat therein during a predetermined period of operation of the switch, said shunt means being a heat-deformable member having a resistance such that the flow of current therethrough after it has closed the shunt circuit keeps it heated and flexed in circuit closing position.

8. A thermal switch comprising a pair of normally spaced co-operating contacts, means providing a current conducting path shunting said contacts, means responsive to heat produced by current in said path for moving one of said contacts into engagement with the other contact whereby said contacts alternately engage and disengage each other, and extraneous shunting means responsive to the heat accumulated during a plurality of successive intervals of current flow in said path to close a shunt circuit around the said contacts and thereby terminate further operation of the switch.

9. A thermal switch comprising a pair of normally spaced co-operatingcontacts, means providing a current conducting path shunting said contacts, means responsive to heat produced by current in said path for moving one of said contacts into engagement with the other contact whereby said contacts alternately engage and disengage each other, and extraneous shunting means responsive to the heat accumulated during a plurality of successive intervals of current flow in said path to close a shunt circuit around the said contacts and thereby terminate further operation of the switch, said shunting means comprising a bimetallic strip having a resistance such that the flow of current therethrough after it has closed the shunt circuit keeps it heated and flexed in circuit closing position.

10. A thermal switch comprising a pair of normally spaced co-operating contacts, conductive support members for said contacts, at least one of said support members being a bimetallic strip, means providing a current conducting path shunting said contacts and supplying heat to said bimetallic strip to cause it to carry its contact into engagement with the other contact whereby said contacts alternately engage and disengage each other, and an extraneous shunting bimetallic strip mounted with its ends adjacent to but normally spaced from the respective contact support members, said shunting strip being responsive to the heat accumulated during a plurality of successive intervals of current flow in said path to carry its ends into engagement with the respective contact support members and thereby close a shunt circuit around the contacts.

11. A thermal switch comprising a sealed envelope containing an ionizable medium, a pair of bimetallic strips fixedly supported at one end in said envelope and carrying contacts at their free ends, said strips being spaced for a glow discharge therebetween and being arranged to flex toward each other to carry said contacts alternately into and out of engagement with each other, and another slower acting bimetallic strip supported intermediate its ends in position to be heated by said glow discharge and having its free ends adjacent to but normally out of engagement with respective ones of said pair of strips, said slower acting strip being arranged to flex in a direction such that its ends are carried into shunting engagement with said pair of strips upon accumulation of heat therein during a plurality of successive intervals of current flow in the glow discharge, said slower acting strip having a resistance such that the flow of current therethrough keeps it heated and flexed in circuit closing position.

MARK A. TOWNSEND. 

